Tetracycline is a commonly used antibiotic that is prescribed to treat multiple infections and is taken orally. While it primarily treats bacterial infection, it is also effective against some types of parasites and may also be used as a biomarker. Tetracycline may be used to treat bacterial infections in the respiratory or urinary tracts; the intestines; the genitals; the lymph nodes; and other systems in the body. Tetracycline may also be used to treat infections caused by direct contact with infected animals, and it is also used to treat infections from direct contact with contaminated food. When penicillin is contraindicated for serious infections like anthrax or listeria, tetracycline may be used instead. Because of the breadth of its uses, a number of organisms have acquired resistance to tetracycline, thereby limiting its versatility and usage. Initially patented in 1953, tetracycline was introduced commercially in 1978 and is on the World Health Organization’s List of Essential Medicines. Common side effects may include diarrhea, vomiting and nausea, loss of appetite, and rash. If used by young children, under the age of eight, side effects may include stunted tooth development.

The antibiotic family of tetracyclines was discovered in the 1940s. In 1950, the chemical structure was determined and the fermentation process for the substance was patented shortly thereafter. Tetracycline has been marketed as Sumycin, Tetracyn, and Panmycin, among other brands, and it is also available as a generic. It is prescribed to treat infections as wide-ranging as acne, plague, and syphilis, and it is also the preferred treatment for Rocky Mountain Spotted Fever. Tetracycline works by preventing bacteria from making proteins.

The same characteristics of tetracycline that make it an effective biomarker may also cause it to discolor the teeth. When tetracycline bonds with calcium ions, it is incorporated into the cartilage, bone, and teeth. If it is ingested consistently in childhood, when the permanent teeth are developing in the jaw, it can lead to a yellowish or greenish discoloration of the dentine that lies just beneath the tooth enamel; this discoloration is visible through the translucent enamel and appears fluorescent under ultraviolet light. As tetracycline oxidizes, the stained teeth turn brown and are no longer fluorescent under ultraviolet light.

Calcium ions render tetracycline ineffective, and it is therefore not to be taken with dairy products. It is also inactivated by aluminum, iron, and zinc ions and should therefore not be taken concurrently with antacids or heartburn remedies. Because tetracycline can cause photosensitivity in the skin, exposure to sun and intense light should be avoided. Tetracycline can also lead to drug-induced lupus, hepatitis, fatty liver, kidney problems, and tinnitus, and when expired tetracycline is ingested this can lead to Fanconi syndrome, a serious kidney disorder. It may affect fetal bone growth and should be avoided while pregnant, and it may also lead to breathing complications in certain individuals, sometimes even resulting in anaphylactic shock. Short-term use while breastfeeding is safe, but tetracycline should not be used long term while breastfeeding. Tetracycline may also interfere with the effectiveness of methotrexate.